This study investigates the impact of evidentiality on source monitoring and the impact of source monitoring on false belief understanding (FBU), while controlling for short-term memory, age, gender, and receptive vocabulary. One hundred (50 girls) monolingual 3- and 4-year-olds from Turkey and the UK participated in the study in 2019. In Turkish, children's use of direct evidentiality predicted their source monitoring skills, which, in turn, predicted their FBU. In English, FBU was not related to source monitoring. Combined results from both languages revealed that Turkish-speaking children had better FBU than English-speaking children, and only for Turkish-speaking children, better source monitoring skills predicted better FBU. This suggests an indirect impact of evidentiality on FBU by means of source monitoring in Turkish.